Lighting device and inspection device

ABSTRACT

A lighting device ( 23 ) irradiates a web under conveyance with light. The lighting device includes a light source ( 43 ), and an irradiation port ( 61 ) configured to open linearly in a widthwise direction of the web at an end portion facing the web. The irradiation port ( 61 ) is formed between first and second parallel portions ( 62   b ,  63   b ) where a first plate member ( 62 ) and a second plate member ( 63 ) parallelly face each other. The web under conveyance is irradiated with linear light. It is possible to provide a lighting device capable of irradiating only an inspection region of a sheet or a web with light.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of Application No.17/310,505, filed on Aug. 6, 2021, which is a national phase entry ofPCT Application No. PCT/JP2020/004799, filed on Feb. 7, 2020, whichclaims priority to Japanese Application No. 2019-021242, filed on Feb.8, 2019, which applications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a lighting device configured toirradiate a pattern printed on a sheet or a web with light, and aninspection device including the lighting device.

BACKGROUND

Some conventional printing presses include an inspection deviceconfigured to measure the density of a color after printing using adevice called an inline density measuring device and determine qualityof printing using the density. A conventional inline density measuringdevice is described in, for example, patent literature 1.

In the inline density measuring device disclosed in patent literature 1,a color bar on a sheet-like object conveyed after printing is capturedby a camera, and the color measurement value (RGB value) of obtainedimage data is converted into a converted density value by calculation.If the difference between the converted density value and apredetermined reference density value serving as a determinationcriterion falls within an allowable range, the inspection devicedetermines that the quality is high.

To convert the color measurement value into the converted density value,a conversion formula is used. The conversion formula is created usingthe reference density value obtained by reading the color bar using adedicated mobile densitometer and the color measurement value (to bereferred to as a reference color measurement value hereinafter) of theimage data obtained by capturing the color bar by the camera. Theconversion formula is an equation for calculating the reference densityvalue from the reference color measurement value.

The image data obtained by image capturing using the camera isinfluenced by a pattern on the periphery of the color bar. For thisreason, if the printed pattern changes, the color measurement value ofthe image data captured by the camera is different from the referencecolor measurement value even if the color bar is printed in thereference density value. Hence, in this case, the color measurementvalue of the color bar cannot correctly be measured and, accordingly,the converted density value to be obtained using the conversion formulacannot correctly be obtained. Hence, if the job of the printing press isswitched, and the pattern of the printed product changes, the conversionformula needs to be created again using a reference density valueobtained by reading the color bar using the dedicated mobiledensitometer and a reference color measurement value of image dataobtained by capturing the color bar by the camera.

Citation List Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2013-75519

SUMMARY Technical Problem

In the above-described conventional inline density measuring device,since the image data obtained by image capturing using the camera isinfluenced by the pattern on the periphery of the color bar, theconversion formula needs to be re-created every time the print job isswitched. Hence, the efficiency when switching the print job becomeslow.

It is an object of embodiments of the present invention to provide alighting device capable of irradiating only an inspection region on asheet or a web with light. It is another object of the embodiments ofthe present invention to raise efficiency when switching a print job.

Means of Solution to the Problem

In order to achieve the above objects, there is provided a lightingdevice configured to irradiate one of a sheet and a web under conveyancewith light, comprising a light source, and an irradiation port whichopens linearly in a widthwise direction of one of the sheet and the webat an end portion facing one of the sheet and the web, wherein theirradiation port is formed between parallel portions where a first platemember and a second plate member parallelly face each other, and one ofthe sheet and the web under conveyance is irradiated with linear light.

According to embodiments of the present invention, there is provided aninspection device comprising a lighting device according to embodimentsof the present invention, an imaging unit configured to capture a colorbar printed on one of a sheet and a web in a state in which the colorbar is irradiated with light of the lighting device during conveyance ofone of the sheet and the web, a type detection unit configured to detecta type of one of the sheet and the web, an acquisition unit configuredto acquire a color measurement value of image data captured by theimaging unit, a storage unit configured to store a correction value foreach type of one of the sheet and the web, a calculation unit configuredto read out, from the storage unit, the correction value correspondingto the type of one of the sheet and the web detected by the typedetection unit and obtain a density value of the color bar bycalculation using the correction value and the color measurement valueacquired by the acquisition unit, and a determination unit configured todetermine quality by comparing the density value with a determinationcriterion value.

Effect of Embodiments of the Invention

In embodiments of the present invention, it is possible to irradiateonly an inspection region on a sheet or a web with light of a lightingdevice. For this reason, when capturing a color bar, the color bar canbe captured by an image capturing device without any influence of apattern on the periphery of the color bar, and image data of the colorbar in original colors can be obtained by image capturing. Hence, sincethe conversion formula need not be re-created when switching the printjob, it is possible to provide a lighting device capable of raisingefficiency when switching the print job.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a web offset printing press including alighting device and an inspection device according to an embodiment ofthe present invention.

FIG. 2 is an enlarged side view of a part of the printing press.

FIG. 3 is a plan view showing a color bar.

FIG. 4 is a rear view showing the lighting device viewed from a cameraside.

FIG. 5 is a side view of the lighting device.

FIG. 6 is a sectional view of the lighting device taken along a lineVI - VI in FIG. 4 .

FIG. 7 is a plan view of a camera.

FIG. 8 is a block diagram showing the configuration of the inspectiondevice.

FIG. 9 is a side view of a sheet-fed offset printing press according toanother embodiment.

FIG. 10 is an enlarged side view showing the main part of the sheet-fedoffset printing press.

FIG. 11 is a side view of a sheet-fed offset printing press according tostill another embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS First Embodiment

A lighting device and an inspection device according to an embodiment ofthe present invention will now be described in detail with reference toFIGS. 1 to 8 . In this embodiment, an example in which the presentinvention is applied to a web offset printing press is shown.

A web offset printing press 1 shown in FIG. 1 includes a web supply unit2 on the leftmost side in FIG. 1 , and sends a web 3 from the web supplyunit 2 to the right side in FIG. 1 . An infield unit 4 is provided onthe right side of the web supply unit 2, and a printing section 5 isprovided on the right side of the infield unit 4. The printing section 5performs printing on both the obverse and reverse surfaces of the web 3by first to fourth printing units 6 to 9. On the downstream side of theprinting section 5 along the conveyance direction of the web 3, a dryingunit 10, a cooling unit 11, and a folding machine 12 are arranged inthis order. A web path unit 13 is provided on the upper side of thecooling unit 11. The web 3 is sent from the web path unit 13 to thefolding machine 12.

As shown in FIG. 2 , the web path unit 13 employs a structure configuredto send the web 3 wound around a plurality of rollers 21 to the upperside. In the lower portion of the web path unit 13, two lighting devices23 and two cameras 24, which form a part of an inspection device 22 (seeFIG. 8 ) according to the embodiment of the present invention, areprovided. The lighting devices 23 and the cameras 24 are arranged at twopoints apart in the vertical direction in the web path unit 13. Thelighting device 23 on the lower side irradiates the obverse surface ofthe web 3 advancing upward in the web path unit 13 with light obliquelyfrom above. The lighting device 23 on the upper side irradiates thereverse surface of the web 3 advancing upward in the web path unit 13with light obliquely from above.

The camera 24 on the lower side captures, from the horizontal direction,the web 3 irradiated with light by the lighting device 23 on the lowerside, and sends image data to a control device 25 (see FIG. 8 ) to bedescribed later. The configuration of the control device 25 will bedescribed later. The camera 24 on the upper side captures, from thehorizontal direction, the web 3 irradiated with light by the lightingdevice 23 on the upper side, and sends image data to the control device25. Each of the cameras 24 is formed by a line camera and cansimultaneously capture the web 3 from one end to the other end in thewidthwise direction.

The camera 24 according to this embodiment captures a color bar 26provided in a margin portion near a printed portion 3 a of the web 3, asshown in FIG. 3 . FIG. 3 shows an end portion of the web 3 that has beencut off. The color bar 26 extends in a predetermined width D1 from oneend portion to the other end portion of the web 3 in the widthwisedirection (the left-and-right direction in FIG. 3 ), and is formed by anumber of color patches 26 a arranged in the widthwise direction. Eachcolor patch 26 a is printed such that a predetermined density of, forexample, 100% can be obtained as a color density by the first to fourthprinting units 6 to 9.

As shown in FIG. 4 , the lighting device 23 is formed into an elongatedshape extending from one end side to the other end side of the web 3 inthe widthwise direction (the left-and-right direction in FIG. 4 ) whenviewed from the camera side, and its two end portions in thelongitudinal direction are attached to a pair of frames 31 and 32 of theprinting press 1 via a support frame 33. The support frame 33 isstretched between the pair of frames 31 and 32 of the printing press 1and swingably supported by the frames 31 and 32 via support shafts 34.The support shafts 34 are connected to the lower end portion of thesupport frame 33. Hence, as shown in FIG. 5 , the support frame 33 canswing between a use position indicated by a solid line in FIG. 5 and aretreat position indicated by an alternate long and two short dashedline in FIG. 5 .

Each of the frames 31 and 32 is provided with an upper stopper 35 and alower stopper 36 to define the position of the support frame 33. Theupper stopper 35 regulates falling of the support frame from the useposition to the side of the web 3. Lock pins 38 that detachably engagewith engaging members 37 (see FIG. 4 ) of the frames 31 and 32 areprovided at the upper end portion of the support frame 33 at the useposition. When the lock pins 38 are inserted into and engage with theengaging members 37, the support frame 33 is held at the use position.When the lock pins 38 are removed from the engaging members 37 anddisengaged, the support frame 33 can swing from the use position to theretreat position. The support frame 33 according to this embodimentincludes handles 39 to be held by both hands of an operator (not shown)at the time of swing.

The lower stopper 36 supports, from the lower side, the support frame 33that has swung to the retreat position, and regulates downward swing ofthe support frame 33 from the retreat position.

As shown in FIG. 6 , the lighting device 23 is equipped with abox-shaped housing 41 with an opening on one of its sides, a lightshielding member 42 attached to the opening of the housing 41, a lightemitting device 44 including a light source 43 and stored in the housing41, and the like.

As shown in FIG. 4 , the housing 41 is formed long in the widthwisedirection of the web 3. In the longitudinal direction of the web 3, thelength of the housing 41 is longer than the width of the web 3. The twoend portions of the housing 41 in the longitudinal direction areattached to the support frame 33 via brackets 45 (see FIG. 5 ). Thehousing 41 is attached to the bracket 45 by threadably engaging aplurality of attachment bolts 46 extending through the bracket 45 withthe housing 41, as shown in FIG. 5 . In this embodiment, arc-shaped longholes 47 configured to pass the attachment bolts 46 are formed in thebracket 45 such that the attachment angle of the housing 41 can bechanged.

As shown in FIG. 6 , the light shielding member 42 includes, at its endportion facing the web 3, an irradiation port 61 that opens linearly inthe widthwise direction of the web 3. The light shielding member 42according to this embodiment includes a first plate member 62 attachedto the upper portion of the housing 41 in FIG. 6 , and a second platemember 63 attached to the lower portion of the housing 41 in FIG. 6 .

The pair of first and second plate members 62 and 63 are formed bybending plates made of a metal such that these are parallel to eachother. In addition, the first and second plate members 62 and 63 areformed with the same length as the housing 41 in the widthwise directionof the web 3.

Also, the first and second plate members 62 and 63 include first andsecond reflecting portions 62 a and 63 a that are inclined such that thespace between the plate members 62 and 63 gradually becomes narrowerfrom the side of the light source 43 toward the irradiation port 61, andfirst and second parallel portions 62 b and 63 b extending from thedistal ends of the first and second reflecting portions 62 a and 63 a inparallel to an optical axis C of the light emitting device 44.

The irradiation port 61 is formed between the first parallel portion 62b and the second parallel portion 63 b, where the first plate member 62and the second plate member 63 parallelly face each other.

The space between the first parallel portion 62 b and the secondparallel portion 63 b, that is, an opening width D2 of the irradiationport 61 in a direction orthogonal to the widthwise direction of the web3 is narrower than the width D1 (see FIG. 3 ) of the color bar 26 in thedirection orthogonal to the widthwise direction of the web 3. Hence,linear light narrower than the width D1 of the color bar 26 exits fromthe irradiation port 61.

The light emitting device 44 includes the light source 43, a lens 64located on a side of the opening of the housing 41, and air blastmembers 65 located near the light source 43.

The light source 43 is formed by a number of LEDs 43 a. The LEDs 43 aare mounted on a substrate 66 such that the optical axis C isperpendicular to the substrate 66, and are provided while being arrangedat a predetermined interval in the whole region in the longitudinaldirection of the housing 41.

The lens 64 is configured to diffuse light from the light source 43 tothe whole region in the light shielding member 42. Some of the lightdiffused by the lens 64 directly travels toward the irradiation port 61,and most of the remaining light is reflected by the first and secondreflecting portions 62 a and 63 a and sent to the irradiation port 61.For this reason, from the irradiation port 61, the light exits in adirection parallel or almost parallel to the optical axis C, and the web3 is irradiated with linear light having a narrow width in the directionorthogonal to the widthwise direction.

The air blast members 65 blast air sent from an air supply source (notshown). The air blast members 65 are arranged on both sides of the LEDs43 a and supported by the housing 41 such that the air is blasted to theLEDs 43 a. When the air is blasted to the LEDs 43 a, the LEDs 43 a arecooled. Note that the air blast members 65 may be arranged to blast airto the back surface of the substrate 66, as indicated by long and twoshort dashed lines in FIG. 6 .

Since the air blasted from the air blast members 65 passes inside thelight shielding member 42 and is discharged from the irradiation port 61to the outside of the lighting device 23, the air is blasted from theirradiation port 61. The air always flows near the irradiation port 61.This prevents powder dust generated from the web 3 or ink mist generatedin the first to fourth printing units 6 to 9 from entering the lightshielding member 42 via the irradiation port 61, and adhering to thelens 64 or the light source 43 or adhering to the distal end portion ofthe irradiation port 61 and closing the irradiation port 61.

As shown in FIG. 7 , the camera 24 is attached to a support member 67stretched between the pair of frames 31 and 32 of the printing press 1,and arranged at a position corresponding to the center portion of theweb 3 in the widthwise direction.

As shown in FIG. 8 , the inspection device 22 includes a part of thecontrol device 25 configured to control the operation of the printingpress 1, the above-described lighting device 23 and the camera 24, amobile densitometer 71 to be described later, a display device 72, andthe like. The mobile densitometer 71 reads the color bar 26 serving asthe reference of the web 3 cut for each printed portion 3 a (see FIG. 3) by a dedicated image reader (not shown), and measures the density ofeach color patch 26 a from image data obtained by the image reader. Themeasurement result is sent as a reference density value to the controldevice 25. The display device 72 displays the operation state of theprinting press 1, various kinds of alarms, and the like.

The control device 25 includes a printing section 73, an inspectionsection 74, a storage unit 75, and a determination unit 76. The printingsection 73 controls the operations of the drive motor (not shown) andvarious kinds of actuators of the printing press 1.

The inspection section 74 includes a lighting section 81, an imagingunit 82, an acquisition unit 83, a calculation unit 84, and a typedetection unit 85.

The lighting section 81 switches ON/OFF of the light source 43. Theimaging unit 82 includes the camera 24, a circuit (not shown) configuredto control the image capturing operation of the camera 24, and the like,and captures the color bar 26 by the camera 24 during conveyance of theweb 3.

The acquisition unit 83 acquires the color measurement value (RGB value)of the image data captured by the camera 24. The image data is imagedata of each color patch 26 a of the color bar 26.

The calculation unit 84 performs calculation using a conversion formula86 prepared in advance and a correction value 87 stored in the storageunit 75. The conversion formula 86 is an equation for calculating thereference density value measured by the mobile densitometer 71 from areference color measurement value obtained by capturing, by the camera24, the color bar 26 similar to the reference color bar 26 measured bythe mobile densitometer 71. As the conversion formula 86, an equationsimilar to an equation described in, for example, Japanese PatentLaid-Open No. 2013-75519 of prior application by the applicant of thepresent invention can be used. When the conversion formula 86 is used, adensity value can be converted from the color measurement value obtainedby capturing the color bar 26 that is not a reference. The density valueobtained by the calculation will be referred to as a “converted densityvalue” hereinafter.

The correction value 87 is determined for each type of the web 3. If thetype of the web 3 changes, even if printing is performed in the samedensity, the density value changes from the converted density valuebased on the color measurement value obtained by image capturing by thecamera 24. The correction value 87 is a value used to correct acalculation result that changes due to the type of the web 3. That is,when the calculation unit 84 performs calculation using the colormeasurement value of actual image data obtained by image capturing usingthe camera 24 and the above-described conversion formula 86 and thecorrection value 87, a corrected converted density value corrected bythe correction value 87 is obtained.

The data of the type of the web 3 is included in basic data to be usedby the printing section 73 to control a printing operation. The typedetection unit 85 reads out the data of the type of the web 3 from thebasic data.

The storage unit 75 stores the above-described correction value 87 foreach type of the web 3 as a correction processing table.

The determination unit 76 compares the corrected converted density valuewith a predetermined reference density value (determination criterionvalue) serving as a predetermined determination criterion for each colorpatch 26 a. If the difference between the values falls within anallowable range, it is determined that the quality is high. If thedifference falls outside the allowable range, it is determined that thequality is poor. The determination unit 76 displays the qualitydetermination result on the display device 72.

In the printing press 1 including the thus configured inspection device22, when printing is performed on the web 3, the color bar 26 iscaptured by the camera 24 in the web path unit 13, and the determinationunit 76 determines the quality of the ink density based on image dataobtained by the image capturing.

The quality determination is performed by the determination unit 76 bycomparing the corrected converted density value obtained by thecalculation unit 84 using the color measurement value of the actualimage data obtained by image capturing using the camera 24, theconversion formula 86, and the correction value 87 corresponding to thetype of the current web 3 with the reference density value serving asthe determination criterion.

The color measurement value of the actual image data obtained by imagecapturing using the camera 24 does not change even if the patternprinted on the web 3 changes, if the ink supply amounts in the first tofourth printing units 6 to 9 do not change. This is because the lightingdevice 23 irradiates the color bar 26 on the web 3 with linear light,and only the color bar 26 can be irradiated with the light of thelighting device 23. For this reason, the color bar 26 can be captured bythe camera 24 without any influence of the pattern on the periphery ofthe color bar 26, and the image data of the color bar 26 in originalcolors can be obtained by the image capturing.

That the color measurement value of the image data captured using thecamera 24 does not change even if the pattern changes means that it isunnecessary to perform conversion formula re-obtainment that isperformed in the conventional device. Hence, according to thisembodiment, since the conversion formula re-obtainment need not beperformed at the time of print job switching, it is possible to providea lighting device capable of raising efficiency when switching the printjob.

The irradiation port 61 according to this embodiment is formed betweenthe first parallel portion 62 b and the second parallel portion 63 b,where the first plate member 62 and the second plate member 63parallelly face each other. For this reason, since light that is notparallel or almost parallel to the optical axis C is shielded by thefirst plate member 62 and the second plate member 63, the color bar 26is substantially irradiated with parallel light.

As a result, only the color bar portion is irradiated with the light ofthe lighting device 23, and image data is never influenced by diffusedlight from the pattern on the periphery of the color bar 26. Hence,accurate density measurement can be performed, and the frequency ofre-obtaining the conversion formula can be reduced. It is thereforepossible to prevent the web 3 from being wasted and save the work timeneeded for preparation until actual printing.

The lighting device 23 according to this embodiment includes the airblast members 65. It is therefore possible to prevent dirt such as inkmist or powder dust from adhering to the lens 64, the light source 43,or the irradiation port 61 and reduce the maintenance frequency, and itis also possible to maintain high inspection performance and densitymeasurement performance.

Also, since the lighting device 23 includes the air blast members 65, itis possible to suppress a brightness change by cooling the light source43 (LEDs 43 a) with cooling air.

The first plate member 62 and the second plate member 63 according tothis embodiment include the first and second reflecting portions 62 aand 63 a that are inclined such that the space between the plate members62 and 63 gradually becomes narrower from the side of the light source43 toward the irradiation port 61.

For this reason, since the color bar 26 can be irradiated with strong(bright) light from the irradiation port 61, the brightness differencebetween the color bar 26 and the pattern on the periphery becomes large,and the image data is more hardly influenced by the pattern on theperiphery in image capturing. Hence, a density value close to thereference density value measured by the mobile densitometer 71 can beobtained using the camera 24, and the reliability of the determinationresult by the determination unit 76 becomes higher.

The opening width D2 of the irradiation port 61 according to thisembodiment in the direction orthogonal to the widthwise direction of theweb 3 is narrower than the width D1 of the color bar 26 in the directionorthogonal to the widthwise direction of the web 3. According to thelighting device 23, only the color bar 26 is irradiated, and a stableslit light source is generated. Hence, the accuracy of density qualitydetermination becomes higher.

In the inspection device 22 according to this embodiment, if the printjob changes, and the type of the web 3 changes, the type detection unit85 detects the type of the new web 3. Then, the calculation unit 84obtains a corrected converted density value corresponding to the new web3 using the correction value 87 according to the type of the web 3, acolor measurement value obtained by capturing, using the camera 24, thecolor bar 26 printed on the new web 3, and the conversion formula 86.

Hence, according to this embodiment, density measurement can beperformed without correction processing not only in a case in which theprinting material (web 3) does not change, and only the pattern changesbut also in a case in which the printing material changes.

Second Embodiment

A lighting device can be configured as shown in FIGS. 9 and 10 . Thesame reference numerals as in FIGS. 1 to 8 denote the same or similarmembers in FIGS. 9 and 10 , and a detailed description thereof willappropriately be omitted.

A printing press 91 shown in FIG. 9 is a sheet-fed offset printingpress, and a sheet supply unit 93 configured to supply a sheet 92 isprovided at an end portion on the right side in FIG. 9 . The printingpress 91 includes a printing section 100 including first to sixthprinting units 94 to 99, a coating unit 101 located on the downstreamside of the printing section 100 along the conveyance direction of thesheet 92, and a sheet discharge unit 103 configured to dry the sheet 92coated by the coating unit 101 and discharge it to a discharge pile 102.The first to sixth printing units 94 to 99 perform printing on onesurface of the sheet 92.

In this embodiment, a lighting device 23 according to the embodiment ofthe present invention is arranged at a position facing an impressioncylinder 104 in the coating unit 101. As shown in FIG. 10 , the lightingdevice 23 according to this embodiment is arranged immediately above theimpression cylinder 104, and irradiates the upper surface (printedsurface) of the sheet 92 conveyed by the impression cylinder 104 withlinear light. A camera 24 is provided at a position apart upward fromthe impression cylinder 104.

In this embodiment, a color bar 26 on the sheet 92 can be captured bythe camera 24 without any influence of a pattern on the periphery.Hence, according to this embodiment, efficiency when switching the printjob of the sheet-fed offset printing press 91 becomes higher.

Third Embodiment

A lighting device can be configured as shown in FIG. 11 . The samereference numerals as in FIGS. 1 to 8 denote the same or similar membersin FIG. 11 , and a detailed description thereof will appropriately beomitted.

A printing press 111 shown in FIG. 11 is a sheet-fed offset printingpress, and a sheet supply unit 113 configured to supply a sheet 112 isprovided at an end portion on the right side in FIG. 11 . The printingpress 111 includes a printing section 114 configured to performdouble-sided printing, an inspection section 115 provided on thedownstream side of the printing section 114 along the conveyancedirection of the sheet 112, and a sheet discharge unit 120 configured tosend the sheet 112 inspected by the inspection section 115 by achain-type conveyance device 116 and discharge it to a plurality ofdelivery piles 117 to 119.

The printing section 114 includes first to fifth surface printing units121 to 125 configured to perform printing on the obverse surface of thesheet 112, and first to fifth back printing units 126 to 130 configuredto perform printing on the reverse surface of the sheet 112.

The inspection section 115 includes an upstream-side surface inspectionunit 131 and an upstream-side back inspection unit 132, and adownstream-side surface inspection unit 133 and a downstream-side backinspection unit 134.

The upstream-side surface inspection unit 131 and the upstream-side backinspection unit 132 perform inspection of the printing quality of thesheet 112 and density inspection of a color bar 26 using visible lightcameras 135. In this embodiment, a lighting device 23 according to theembodiment of the present invention irradiates the sheet 112 to becaptured by the visible light camera 135 with linear light. The visiblelight camera 135 is the same as the camera 24 used when employing thefirst embodiment.

The downstream-side surface inspection unit 133 and the downstream-sideback inspection unit 134 perform inspection of the printing quality ofthe sheet 112 using ultraviolet cameras 136.

According to this embodiment, it is possible to perform ink densityinspection on both the obverse surface and the reverse surface of thesheet 112. In addition, since the color bar 26 can be captured by thevisible light camera 135 without any influence of a pattern on theperiphery of the color bar 26, efficiency when switching the print jobof the sheet-fed offset printing press 111 becomes higher.

In the above-described embodiments, an example in which the lightingdevice according to the embodiment of the present invention is used in adensity inspection device configured to capture a color bar and inspectthe density of ink has been described. However, the lighting deviceaccording to the embodiment of the present invention is not limited tothis example, and may be used in a pattern inspection device configuredto inspect the presence/absence of a printing failure such as printingomission or dirt adhesion in a printed pattern portion. Even in thiscase, a linear narrow region in an inspection region is irradiated withlight, thereby emphasizing the inspection region without any influenceof a pattern in a non-inspection region and detecting a printing failureaccurately as compared to conventional inspection that irradiates a widerange with light.

EXPLANATION OF THE REFERENCE NUMERALS AND SIGNS

3 . . . web, 23 . . . lighting device, 43...light source,61...irradiation port, 62...first plate member, 62 b...first parallelportion, 63...second plate member, 63 b...second parallel portion, 92,112...sheet

1. A lighting device comprising: a light source; and a light shieldingmember including an irradiation port which opens linearly, wherein thelight shielding member includes a first plate member and a second platemember, the first plate member and the second plate member include afirst parallel portion and a second parallel portion, respectively, thefirst parallel portion and the second parallel portion parallelly faceeach other, and the irradiation port is formed between the firstparallel portion and the second parallel portion and is configured toirradiate a linear region in an inspection region with light, therebyirradiating only the inspection region with the light.
 2. The lightingdevice according to claim 1, further comprising an air blast member forsupplying cooling air to the light source.
 3. The lighting deviceaccording to claim 1, wherein the first plate member and the secondplate member further includes, respectively, each of which is configuredto reflect some of the light from the light source, the first reflectingportion and the second reflecting portion are inclined such that a spacebetween the first plate member and the second plate member graduallybecomes narrower from a side of the light source toward the irradiationport.
 4. An inspection device configured to determine quality of aprinted product, the inspection device comprising: a lighting deviceaccording to claim 1, the lighting device configured to irradiate acolor bar printed on one of a sheet and a web under conveyance withlight, the color bar serving as the inspection region; a cameraconfigured to capture the color bar which is irradiated with light ofthe lighting device; an acquisition circuit configured to acquire acolor measurement value of image data captured by the camera; acalculator configured to calculate a density value of the color barusing the color measurement value acquired by the acquisition circuit;and a determination circuit configured to determine quality by comparingthe density value with a determination criterion, wherein the lightingdevice irradiates the color bar with linear light.
 5. The inspectiondevice according to claim 4, wherein an opening width of the irradiationport in a direction orthogonal to the widthwise direction of one of thesheet and the web is narrower than a width of the color bar in thedirection orthogonal to the widthwise direction of one of the sheet andthe web.
 6. The inspection device according to claim 4, furthercomprising: a type detection unit configured to detect a type of one ofthe sheet and the web; and a storage device configured to store acorrection value for each type of one of the sheet and the web, whereinthe calculator is configured to read out, from the storage device, thecorrection value corresponding to the type of one of the sheet and theweb detected by the type detection unit and calculate a density value ofthe color bar using the correction value and the color measurement valueacquired by the acquisition circuit.